Twist-drill



M. 0. JOHNSON.

TWIST DRILL.

(No Model.)

N0. 329,174. Patented Oct. 27, 1885 \w m x r m 5 AW N, PETERS. Phnlomhogriphcr. Washington. D C,

NITE TATFS MOSES O. JOHNSON, OF HARTFORD, CONNECTICUT.

TWIST- DRILL.

SPECIFICATION forming part of Letters Patent No. 329,174, dated October 2'7, 1885.

Application filed April 9, 1885. Serial No. 161,667.

To all whom it may concern.-

Be it known that I, MosEs O. JoHNsoN, of Hartford, in the county of Hartford and State of Connecticut, have invented a certain new and useful Improvement in Twist-Drills, of which the following is adesoription, reference being had to the accompanying drawings, where Figure 1 is a side view of a twistdrill made in accordance with my improved invention. Fig. 2 is a view in cross-section through the flute of the same on plane denoted by line 00 w of Fig. 1. Fig. 3 is a crosssectional view through the fluted part of the drill near the point on plane denoted by line y y of Fig. 1. Fig. 4 is a diagram View showing a development of the pitch-line in relation to the axis of thedrill.

The object of my invention is to produce a drill that will maintain the proper angle of the cutting-lips under repeated sharpenings, so that when a drill has been once dulled it can be resharpened on a machine a number of times without destroying this proper angle of the cutting-lip, and one that will at the same time properly clear itself; and it consists in a twist-drill having cutting-edges, and having the flute made with the required pitch for a limited distance near the point of the drill, and an increasing pitch from that section to the upper end of the flute, as more particu larly hereinafter described.

In the accompanying drawings, the letter (t denotes a twist-drill having a shank, b, flutes c and c, and the ordinary eutting -lips, d. For a certain section, 6, near the point of the drill, the cutting-edge of the lands 0 has a constant pitch, while for the remaining section, f,of the drill this cutting-edge is made with a gradu- .o ally-increasing pitch. The drill may be made (No model.)

with a web of increasing thickness from the point to the shank, as illustrated in Figs. 3 and 2.

In the diagram view Fig. 4 the axis of the drill is represented by the full line drawn parallel to the drill in Fig. 1. The pitch-line is also shown in full line, the straight portion bounding one side of the section e representing the extent of the true'pitcl1,and the curved line bounding one side of the section frepresenting the increased pitch, its departure from the true pitch being shown by its divergence from the dotted extension of the true pitchline.

The length of the section 6 is not material, except that it should not be so great as to cause the drill to clog on account of lack of clearance, and the increased pitch may be made just sufficient to cause the drill to properly clear itself.

My improved drill possesses all the advantages of the ordinary drill, with a further ad vantage of. increased utility and durability, owing to the readiness with which the drill may be resharpened upon a drill-sharpening machine without requiring changes in the ad justment of the drill-bearing portion of the sharpener to adjust the drill to the particular angle, owing to changes caused by the increased pitch of the flute or land.

I claim as my invention As an improved article of manufacture, a

- twist-drill having grooves wit-h a regular-pitch for a certain distance near the point of the drill and an increased pitch to the upper end of the groove, all substantially as described.

MOSES O. JOHNSON. Witnesses: 1

CHAS. L. BURDETT, H. It. WILLIAMS. V 

